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.TH DDI_PERIODIC_ADD 9F "May 04, 2017"
.SH NAME
ddi_periodic_add \- request periodic function invocation
.SH SYNOPSIS
.nf
#include <sys/dditypes.h>
#include <sys/sunddi.h>

\fBddi_periodic_t\fR \fBddi_periodic_add\fR(\fBvoid (*\fR\fIfunc\fR)(\fBvoid *)\fR, \fBvoid *\fR\fIarg\fR,
     \fBhrtime_t\fR \fIinterval\fR, \fBint\fR \fIlevel\fR);
.fi

.SH INTERFACE LEVEL
illumos DDI specific (illumos DDI)
.SH PARAMETERS
.ne 2
.na
\fB\fIfunc\fR\fR
.ad
.RS 12n
The callback function to be invoked periodically in the specified interval.
.RE

.sp
.ne 2
.na
\fB\fIarg\fR\fR
.ad
.RS 12n
The argument passed to the callback function.
.RE

.sp
.ne 2
.na
\fB\fIinterval\fR\fR
.ad
.RS 12n
The periodic interval time in nanoseconds.
.RE

.sp
.ne 2
.na
\fB\fIlevel\fR\fR
.ad
.RS 12n
The callback function is invoked at this priority level.  If the value of
\fIlevel\fR is zero, the callback function is invoked in kernel context.
If the value is greater than zero, but less than or equal to ten, the callback
function is invoked in interrupt context at the specified interrupt level,
which may be used for real time applications.
.sp
This value must be in range of 0-10, which can be either an integer literal, a
pre-defined macro (\fBDDI_IPL_0\fR, ... , \fBDDI_IPL_10\fR), or the
\fBDDI_INTR_PRI\fR macro with the interrupt priority.
.RE

.SH DESCRIPTION
The \fBddi_periodic_add()\fR function schedules the specified function to be
periodically invoked in the nanosecond interval time.
.sp
.LP
As with \fBtimeout\fR(9F), the exact time interval over which the function
takes effect cannot be guaranteed, but the value given is a close
approximation.  If the callback function has not finished execution when the
next interval expires, the system will skip running the callback for that
interval.
.SH RETURN VALUES
\fBddi_periodic_add()\fR returns the non-zero opaque value
(\fBddi_periodic_t\fR), which is later used to cancel the periodic request
with \fBddi_periodic_delete\fR(9F).
.SH CONTEXT
The \fBddi_periodic_add()\fR function may be called from user or kernel
context.
.SH EXAMPLES
\fBExample 1 \fRUsing \fBddi_periodic_add()\fR for a periodic callback function
.sp
.LP
In the following example, the device driver registers a periodic callback
function invoked in kernel context.

.sp
.in +2
.nf
static void
my_periodic_func(void *arg)
{
         /*
          * This handler is invoked periodically.
          */
         struct my_state *statep = (struct my_state *)arg;

         mutex_enter(&statep->lock);
         if (load_unbalanced(statep)) {
                 balance_tasks(statep);
         }
         mutex_exit(&statep->lock);
}

static void
start_periodic_timer(struct my_state *statep)
{
         hrtime_t interval = CHECK_INTERVAL;

         mutex_init(&statep->lock, NULL, MUTEX_DRIVER, DDI_IPL_0);

         /*
          * Register my_callback which is invoked periodically
          * in CHECK_INTERVAL in kernel context.
          */
          statep->periodic_id = ddi_periodic_add(my_periodic_func,
              statep, interval, DDI_IPL_0);
.fi
.in -2

.sp
.LP
In the following example, the device driver registers a callback function
invoked in interrupt context at level 7.
.sp
.in +2
.nf
/*
 * This handler is invoked periodically in interrupt context.
 */
 static void
 my_periodic_int7_func(void *arg)
 {
          struct my_state *statep = (struct my_state *)arg;
          mutex_enter(&statep->lock);
          monitor_device(statep);
          mutex_exit(&statep->lock);
  }

  static void
  start_monitor_device(struct my_state *statep)
  {
          hrtime_t interval = MONITOR_INTERVAL;

          mutex_init(&statep->lock, NULL, MUTEX_DRIVER, DDI_IPL_7);

          /*
           * Register the callback function invoked periodically
           * at interrupt level 7.
           */
          statep->periodic_id = ddi_periodic_add(my_periodic_int7_func,
              statep, interval, DDI_IPL_7);
    }
.fi
.in -2

.SH SEE ALSO
.BR cv_timedwait (9F),
.BR ddi_intr_get_pri (9F),
.BR ddi_intr_get_softint_pri (9F),
.BR ddi_periodic_delete (9F),
.BR qtimeout (9F),
.BR quntimeout (9F),
.BR timeout (9F),
.BR untimeout (9F)
.SH NOTES
The caller must specify \fIinterval\fR as an even, non-zero multiple of 10ms.
No other values are supported at this time. The interval specified is a lower
bound on the interval between executions of the callback.
